U.S. Pat. No. 4,637,144 discloses an apparatus for checking the diameter of crankpins orbiting about a geometrical axis, in the course of the machining in a grinding machine. The apparatus is supported by a support fixed to the worktable of the grinding machine, or by a support affixed to the bed of the grinding machine, or by a longitudinal slide arranged on the worktable.
The apparatus comprises a reference device, Vee-shaped or of another type, for cooperating with the crankpin to be checked, a measuring head fixed to the reference device and provided with two movable arms carrying feelers for contacting diametrically opposite points of the crankpin, a cylinder and piston device, and a coupling device between the cylinder and the support of the apparatus. The reference device is supported by the piston rod and thus is movable along the geometric axis of the cylinder. Moreover, the reference device can rotate, with the cylinder, about an axis of rotation defined by the coupling device and parallel to the geometric axis whereabout the crankpin rotates. The cylinder and piston device comprises a spring, that acts on the piston so as to urge the reference device towards the crankpin to be checked, and a hydraulic or pneumatically actuated device for displacing the piston towards a rest position, in opposition to the force of the spring. In the course of the checking operation, the apparatus is located, with respect to the workpiece, substantially at the opposite side with respect to the one where the grinding wheel is located.
The apparatus and its applications in a grinding machine, described in the formerly mentioned patent, are subject to some inconveniences like considerable layout dimensions, in particular in a transversal direction, high forces of inertia, the impossibility of displacing in an automatic way the reference device from the rest position to the measuring position while the piece (crankshaft) is rotating. These inconveniences are due to both the structure of the apparatus and its application in the machine. All the applications described in the patent involve, in the course of the measurement taking, that the reference device describes a trajectory basically corresponding to the orbital motion of the crankpin.
U.S. Pat. No. 4,351,115 discloses a machine for the dimensional checking of a crankshaft, comprising devices for checking the crankpins in the course of their orbital motion about the main geometrical axis of the crankshaft. Each of these checking devices comprises a guide and reference device, supported by the machine frame, by means of two arms, rotating reciprocally and with respect to the frame, about two axes of rotation parallel to the geometrical axis of the orbital motion. This machine and its associated checking devices are not suitable for checking during the machining operation, among other things owing to the fact that the guide and reference devices describe trajectories that essentially correspond to the orbital motion of the associated crankpin, the speed of the orbital motion is considerably lower with respect to that occurring in the course of the machining in a crankpin grinding machine and the displacement of the checking devices from a rest position to an operating condition occurs when the crankshaft is not rotating.
U.S. Pat. No. 3,386,178 discloses an apparatus, for checking the diameter of cylindrical workpieces, rotating about their geometrical axis, in the course of the machining in a grinding machine. The apparatus comprises two arms, rotating reciprocally and with respect to the grinding-wheel slide. One of the arms supports two reference elements or fixed (with respect to the arm) feelers for contacting the surface of the rotating workpiece and a movable stem, with a feeler for contacting the workpiece and an opposite end for cooperating with the movable element of a clock comparator. The apparatus is manually displaced from a rest position to a measuring condition, and vice versa. The grinding machine cannot machine workpieces rotating with an orbital motion, nor is the measuring apparatus suitable for a similar type of application.